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A5793 - Fibroblast Growth Factor 2 Decreases Bleomycin-Induced Pulmonary Fibrosis Through Inhibition of Fibroblast Collagen Production
Author Block: R. Guzy1, L. El-Baz1, H. Koo1, S. House2, S. Cilvik3, N. O. Dulin4, D. Ornitz3; 1Medicine, The University of Chicago, Chicago, IL, United States, 2Emergency Medicine, Washington University School of Medicine, St. Louis, MO, United States, 3Developmental Biology, Washington University School of Medicine, St. Louis, MO, United States, 4Univ of Chicago, Chicago, IL, United States.
Rationale: Fibroblast Growth Factor (FGF) signaling has been implicated in the pathogenesis of pulmonary fibrosis and as potential reparative factor following lung injury. Mice lacking FGF2 have increased mortality and impaired epithelial recovery after bleomycin, supporting a protective or reparative function following lung injury. We hypothesized that FGF2 overexpression would improve recovery from bleomycin injury. Methods: We developed an inducible genetic system to express FGF2 in type II pneumocytes. Double transgenic (DTG) mice with doxycycline-inducible overexpression of FGF2 (SPC-rtTA; TRE-hFGF2) or single-transgenic controls were administered intratracheal bleomycin and fed doxycycline chow starting at either day zero or seven. To test the effect of FGF2 in vitro, primary mouse and human lung fibroblasts (HLFs) were treated with recombinant FGF2 (2 nM) with or without TGFβ1 (2 ng/ml). Results: Overexpression of FGF2 in mouse lungs for up to 5 months did not result in histologic abnormalities. Compared to controls, doxycycline-induced DTG mice had decreased Collagen 1 (Col1a1), Collagen 3 (Col3a1), and connective tissue growth factor (Ctgf) expression, decreased number of alpha smooth muscle actin (αSMA) positive fibroblasts, and decreased pulmonary fibrosis 21 days post-bleomycin. The reduction in pulmonary fibrosis was seen when FGF2 overexpression was started both at day zero and seven post-bleomycin. FGF2 overexpression did not result in altered whole lung epithelial gene expression, broncho-alveolar lavage (BAL) cellularity, or BAL total protein. In vitro, FGF2 strongly inhibited baseline expression of alpha smooth muscle actin (Acta2), Col1a1, and Ctgf in primary mouse lung fibroblasts, and TGFβ1 induced expression of COL1A1, LOX, and ACTA2 in primary human lung fibroblasts. The effect of FGF2 was completely abolished by PD173074, a FGFR-specific tyrosine kinase inhibitor. While FGF2 did not suppress phosphorylation of Smad2 or Smad-dependent gene expression, FGF2 inhibited TGFβ1-induced stress fiber formation and serum response factor (SRF) luciferase reporter activity. Conclusions: In summary, overexpression of FGF2 is well tolerated and reduces bleomycin-induced pulmonary fibrosis in vivo when given as both a preventative and treatment protocol. FGF2 does not alter either inflammation or whole lung epithelial gene expression post-bleomycin. FGF2 reverses TGFβ1-induced collagen and αSMA expression and stress fiber formation in vitro. These results suggest that FGF2 is antifibrotic through a direct action on lung fibroblasts, leading to decreased collagen expression and differentiation of fibroblasts to myofibroblasts.